Coupling system



July 28, 1936. H. A. WHEELER Er AL COUPLING SYSTEM Fild Nov. 19, 1935 mwm N I IX: l

INVENTORS HAROLD A.WHEELER, JDARNIEL E. HgEETT.

ATTORNEY.

Patented July 1936 Barnett, Tuckahce, N. Y'., assignors to tine Corporation, a corporation of Delaware Application November 19, 1935, Serial No. 50,502

15 Claims.

This invention relates to a circuit arrangement for selectively coupling to a tuned circuit or system any one of a plurality of associated circuits having impedance characteristics of different kinds. While the invention is of general application, it is particularly suitable for coupling different types of antenna circuits to the first tunable circuit of a radio receiver.

It is well known that in coupling an input circuit to a tuned or tunable circuit there is a tendcncy for the impedance of the input circuit to be reflected in some degree into the tuned circuit and alter its resonant frequency. In the design of such a coupling arrangement, therefore, it is highly desirable to minimize the impedance refiected thereby from the input circuit to the tuned circuit, at the same time, however, providing sumcient coupling to secure the desired signal transfer.

This is particularly true in the design of a coupling arrangement for interconnecting an antenna and the first tuned circuit of a radio receiver in which provision must be made to insure thatthe alternative use of antennas of difierent types or designs does not substantially afiect the resonant frequency of the tuned circuit and especially that it does not, if the first tuned circuit is tunable, affect the alignment thereof in a predetermined relation to other circuits tunable conjointly therewith.

One common type of antenna is a capacitive antenna. This is defined as an antenna having an impedance characteristic which is mainly capacitive over the range of frequencies utilized. A

having an impedance characteristic the mean value of which over the range of frequencies utilized is mainly resistive. An example of such a system is that described in a copending application of Harold A. Wheeler, Serial No. 25,735, filed June 10, 1935, for Wave-signal-collecting systems. Such a system may comprise a doublet antenna, an antenna filter, 'a transmission line and a receiver filter connected in the order named, the

receiver filter being adapted for coupling to the first tuned circuit of the radio receiver, preferably with optimum coupling, in 'order to provide the most desirable normal operation. It is also preferable to maintain this condition of optimum coupling for all frequencies within the tuning range of the tuned circuit. Another example of .5

a mainly resistive antenna is a long wire whose length is greater than a quarter wavelength of the received signal wave.

Inasmuch as the design of a coupling arrangement for the first tuned circuit of a radio receiver is materially diiferent for coupling with a mainly capacitive source than for coupling with a mainly resistive source, the manufacturer of radio receivers for users, some of whom may employ a mainly resistive antenna and others of whom may employ a mainly capacitive antenna, is faced with the problem 'of devising some means by which the receiver is readily adaptable for use with antenna of either type.

It is an object of this invention to provide a cirstantialiy the resonant frequency of the tuned circuit or system.

It is another object of this invention to provide such a coupling arrangement readily adapted for alternatively coupling the same radio receiver to either of two antennas having different and approximately predetermined impedance characteristics without substantially ailecting the resonant frequency of the first tuned circuit thereof.

It is a further object of the invention to provide 36 a coupling arrangement for coupling alternatively a capacitive antenna or a resistive antenna to the first tuned circuit of a radio receiver so that each antenna, when eflectively coupled to such tuned circuit, is coupled in the manner preferred for so that type of antenna; so that the change from one antenna to the other does not substantially afiect the resonant frequency of the first tuned circuit; and so that, when the first tuned circuit is tunable, the alignment thereof with respect to other tuned circuits tunable conjointly therewith is not substantially altered.

Other objects of the invention will become apparent upon consideration of the following specification taken in conjunction with the accompanying drawing and the appended claims.

The illustrated embodiment of the invention contemplates a radio receiver having two different coupling circuits associated with the first tunable circuit thereof, one for coupling a capaci- I so.

tive antenna and the other for coupling a resistive antenna to this circuit. The impedance characteristics of these two coupling circuits are so proportioned that the connection of either antenna to its respective coupling circuit causes substantially the same change of the resonant frequency of the first tunable circuit. In the preferred embodiment of the invention, the capacitive-antenna coupling circuit includes capacitance in common with the first tunable circuit while the resistive-antenna coupling circuit includes at least a portion of the reactance of the coupling capacitance for the capacitive antenna and also other impedances individual thereto. Such other impedances may include an inductance inductively coupled to the inductance of the first tunable circuit and capacitance serially connected with such inductance, the several impedances of the resistive-antenna coupling circuit being proportioned to provide optimum coupling between such antenna system and the first tunable circuit, over the tuning range: thereof.

The single figure of the drawing is a circuit diagram, partly schematic, illustrating an embodiment of the invention as incorporated in a tun-' able radio receiver especially adapted to operate either from a simple capacitive antenna or from a doublet antenna with antenna filter, transmission line and receiver filter.

The radio receiver I2 comprises a tunable radio-frequency portion I 3 and succeeding tunable signal-translating portions of conventional character indicated in block form at I4. The receiver is adapted to be used with either a mainly capacitive antenna l6, such as an ordinary singlewire antenna, or with a mainly resistive antenna system I6 comprising a doublet antenna 20, an impedance matching antenna filter 2|, a transmission line 22 and an impedance matching receiver filter 23 connected in the order named. Illustrative of one such resistive antenna systern is that disclosed in the previously mentioned application Serial No. 25,735.

Antenna system I6 is referred to as a resistive to the receiver has a mean value which approximates a pure resistance. This is to be distinguished from the ordinary single-wire antenna in that the latter has an impedance characteristic approximating that of a condenser. For

reference, resistance is indicated in dotted lines across the output terminals A, G of receiver filter 23"to represent the mean impedance of antenna system l6 as measured across its output ter- Lik'ewise, capacitance 25 is indicated in dotted lines between ground and -the terminal or antenna l6 to represent the mainly capacitive impedance characteristic of antenna l6.

Receiver I2 is provided with three input terminals 26, 21, and 23, terminals 26 and 28 being 'for connection respectively to the A and G terminals of the receiver filter 23, terminal 26 being for connection to ground as indicated at 36, and terminal 21 being for connection to the lead-in terminal of antenna l6. To indicate that the receiver is to be used alternatively with either antenna I6 or l6 but not with both at the'same time, a switch 3| is illustrated, antennas l6 and I8 being individually effectively connected with the receiver when switch 3| is in the upper and lower positions; respectively. If only one type of antenna isto be used in a given installation, it may be preferable to omit the switch 3i, providing only the terminals 26, 21, and 28 for appropriate connectionin that installation. The tunableradiofrequency portion l3 includes the first tuned citcuit 34 connected to the input terminals of the first vacuum tube 35 of the radio receiver l2.

The first tuned circuit 34 includes a fixed inductance 36 across which are connected in series fixed condensers 31, 36 and the variable condenser 40. The latter is indicated as tunable by unicontrol means 4| which also operates a variable condenser 42, representative of the succeeding tunable circuits of the receiver.

The coupling circuit for coupling the capacitive antenna l6 to the tuned circuit 34 is essentially of the form described in the previously mentioned' Patent 1,943,405 and includes the condensers 31, 36 included inthe tuned circuit 34.

The bias for the grid of vacuum tube 35 is provided in the usual manner by means (not shown) connected to the terminal 45, the bias being applied througha resistor 44 having high im pedance at radio frequencies.

The eifective capacitanceoi' condensers 31 and 36 in series is preferably much greater than (on the order of 5 to 20 times) the maximum capacitance of tuning condenser 46. This arrangement assures that the antenna I 6, within a reasonable range of dimensions, will not have excessive effect on the resonant frequency of the tuned circuit.

The coupling circuit for coupling the resistive antenna system I8 to the tuned circuit 34 includes in series a coupling condenser 50, inductance 5| inductively coupled to the inductance 36 of the tuned circuit, and the condenser 38 of the tuned circuit 34. The polarity of coupling between inductances 36 and 5| is chosen so that this coupling aids the capacitive coupling of condenser 38. antenna system because the impedance presented The inductance 5] and condenser 50 resonate at a frequency substantially above the tuning range of tuned circuit 34 so that the coupling circuit forthe resistive antenna system has substantial net capacitive reactance at all frequencies in the tuning range.

The relative proportions of the elements of the coupling circuits for the antenna l6 and'the antenna system l8, respectively, in conjunction with the characteristic impedances of such antennas, are such that the connection of either antenna to the receiver l2 causes substantially the same effect on the resonant frequency of tuned circuit 34, and further are such thatthe antenna system [8 is coupled to the tuned circuit 34 with optimum coupling.

The actual proportioning of the elements of the coupling circuits, particularly those ofthe coupling circuit for the resistive antenna, can be determined by the aid of the following rules. In applying these rules, the major considerations are the effect of each element on the coupling between the antennas and the tuned circuit on one hand, and, on the other hand, the efiect on the resonant frequency of the tuned circuit caused by either antenna when coupled thereto.

The amount of coupling between the resistive antenna system I 6 and the tuned circuit 34 is determined primarily by the capacitance C3; of condenser 38 and the mutual inductance M5i-36 between coils 5| and 36. Decreasing Caa or increasing Mei-as has the eflect of increasing the coupling and also the change of resonant frequency of the tuned circuit 36 when the antenna system it is connected thereto. Changing Cao has relatively more eflect atlower frequencies, while changing Mar-3e has relatively more effect athigher frequencies. The capacitance Cso of condenser 59 and the self-inductance L51 of coil 5! have a secondary eflect on the amount of coupling and the change of the resonant frequency of the tuned circuit 36 when the antenna system I8 is connected thereto. Decreasing Cso has the eifect of decreasing the amount of coupling-and also the change of the resonant frequency. Increasing Lsl (without increasing Moi-35) has the effect of increasing the amount of coupling and the change of the resonant frequency. Changing Cso has relatively more effect at lower frequencies while changing Isl has relatively more effect at higher frequencies.

There are thus four degrees of freedom in the design of the coupling system for the resistive antenna system l8. This is 'a suillc'ient number to permit proportioning the circuit to secure the following two results. Firstly, two degrees of freedom arerequired to proportion the effect on the resonant frequency of the circuit til caused by coupling the resistive antenna system is thereto to equal that caused by coupling the capacitive antenna i5 thereto at both the higher and the lower frequencies of thetuning range. secondly, two more degrees of freedom are required to secure optimum coupling to the resistive antenna system is at both the higher and lower frequencies. There is no particular order of procedure which is suggested for properly determining the four values relating to the coupling circuit for the resistive antenna system it. It is not generally required to adjust these values very precisely because both 'the coupling and the effect on the resonant frequency are relatively noncritical, the latter usually being a very small fraction of the resonant frequency. It is an essential requirement, however, that the above four factors have different efiects on the response of the system.

The amount of coupling between the capacitive antenna it and the tuned circuit as is determined by the capacitance of condensers 8? and as in series. In general, it is desired to maintain this capacitance substantially at a predetermined value regardless of the value that may be selected for the capacitance of condenser 88 in accordance with the considerations discussed above. As a consequence, when C3815 changed in one sense in determining the amount of the coupling between the resistive antenna system as and the tuned circuit 35, C31 is usually changed in the opposite sense. to an extent necessary to maintain constant the series capacitance of the two condensers.

It is to be noted that an antenna system ineluding a doublet, filters and connecting transmission line, such as herein described and shown, is not the only type of resistive antenna. A simple single-wire antenna much longer than one quarter of the wavelength of the received signal wave has an impedance characteristic whose mean value over a range of frequencies is mainly resistive.

The means herein disclosed-and claimed for coupling a tuned circuit to either a capacitive or a resistive source with substantially the same effect on the resonant frequency of the tuned circuit, is not limited to coupling the first tuned circuit of a radio receiver to diiferent types of antennas, but is equally applicable to coupling the radio frequency system of a radio transmitter to different types of antennas, and in fact is of general application to any tuned circuit having 5 associated circuits of diflerent impedance characteristics alternatively coupled thereto. and whether or not such associated circuits are sources of excitation thereof.

In order to illustrate the relative magnitudes 1c of the various circuit elements of a typical radio receiver having means in accordance with this invention for adapting it for use with either a capacitive or a resistive antenna, the following approximate values for the tuned and coupling 15 circuits, and other pertinent information, are given for an arrangement of the type herein shown and described.

Tuning range, 550 to 1500 kilocycles.

Capacitance of capacitive antenna, 016:200 20 mlcro-microfarads.

Mean resistance of resistive antenna system, R1a=400 ohms.

Ls1=4.5 microhenries. L3c=220 microhenries.

Moi-36:9 microhenries.

Cas=4800 micromicrofarads.

Cri=i800 micro-microf.

Cao=820 micro-microfarads.

C4o=50-50 micro-microfarads (including in- 30 herent capacitance of the circuits connected thereto).

Rn=100,0ilo ohms.

Cie=.o2 microfarad.

Rar=l0,000 ohms.

While we have described what we at present consider the preferred embodiment of our invention. it will be obvious to those skilled in the art that various changes and modifications may be made therein withoutfdeparting from our invention, and we, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What is claimed is:

1. An electric circuit arrangement for coupling to a resonant circuit any one of a plurality of circuits having predetermined impedance characteristics of substantially difierent kinds, com-. prising a plurality of coupling circuits corresponding, respectively, to said first-named plurality of circuits, each of said coupling circuits being coupled to said resonant circuit and including provisions for connection to its respective firstnamed circuit,,the impedance characteristics of said coupling circuits being so proportioned that the connection of any of said first-named circuits to-its respective coupling circuit causes substantially the same eiiect on the resonant frequency of said resonant circuit. 60 2. An electric circuit arrangement adapted for alternatively coupling to a resonant circuit a circuit having a predetermined mainly resistive impedance or a circuit having a predetermined mainly capacitive impedance, comprising two difc5 ierent coupling circuits corresponding, respectively,- to said first-named circuits, each of said coupling circuits being coupled to'said resonant circuit and including provisions for connection to its respective first-named circuit, the impedance 70 characteristics of said coupling circuits being so proportioned that the connection oi'either of said first-named circuits to its respective coupling cir-. cult causes substantially the same efiect on the resonant frequency of said resonant circuit.

' 3. An electric circuit arrangement for alternatively coupling to a tuned radio-frequency circuit proportioned that the connection of either of be coupled to any one of a plurality of circuitssaid antenna circuits to its respective coupling circuit causes substantially the same effect on theresonant frequency of said tuned circuit.

4. In combination, a tuned circuit adapted to having impedance characteristics of different kinds, and a plurality of coupling circuits corresponding, respectively, to saidfirst-named circuits, eachof said circuits being coupled to said tuned circuit and including provisions for connection to its respective first-named circuit, theimpedance characteristics of said coupling cir-' cuits being so proportioned that the connection of any of said first-named circuits to its respective' coupling circuit causes substantially the same effect on the resonant frequency of said tuned circuit.

5. In combination, a tuned circuit adapted to be alternatively coupled to either of two circuits having respectively a mainly resistive and a mainly reactive impedance characteristic, and two coupling circuits corresponding, respectively, to said first-named circuits, each of said circuits being coupled to said tuned circuit and including provisions for connection to its respective firstnamed circuit, the impedance characteristics of said coupling circuits being so proportioned that the resistive first-named circuit, when effective, is optimum coupled to-said tuned circuit and that either coupling circuit in connection with its respective first-named circuit causes substantially the same effect on the resonant frequency of said tuned circuit.

6. In combination, -a tuned circuit adapted to be alternatively coupled to either of two circuits having impedance characteristics of different kinds, and two coupling circuits corresponding, respectively, to said first-named circuits, each of said circuits being coupled to said tuned circuit having respectively a mainly resistive and a main- 1y reactive impedance characteristic, and two coupling circuits corresponding, respectively, to said first-named circuits, each of said circuits being coupled to said tuned circuit and including provisions for connection to its respective first-named circuit, the impedance characteristics of said coupling circuits being so proportioned that either first-named circuit in connection with its respective coupling circuit reflects into said tuned circuit reactance of the same kind and of substantially the same magnitude. 8. In combination, a tuned circuit' adapted to be alternatively coupled to either of two circuits having respectively a mainly resistive and a mainly reactive impedance characteristic, and two coupling circuits corresponding, respectively, to said first-named circuits, each of said cir- .tunable circuit within the tuning rangethereof.

cuits being coupled to said tuned circuit and including provisions for connection to its respective first-named circuit, the coupling circuit for the reactive first-named circuit including reactance in common with said tuned circuit, and g the coupling circuit for the resistive first-named circuit including. at least a part of said common reactance and also other reactance individual thereto, the impedances of said coupling circuit reactances for the resistive first-named circuit 10 being so proportioned that the connection of either of said first-named circuits to its respective coupling circuit causes substantially the same effect on the resonant frequency of said resonant circuit.

9. In combination, a tuned circuit adapted to' be alternatively coupled to either of two circuits: having respectively a mainly resistive and a mainly reactive impedance characteristic, and two coupling circuits corresponding, respectively, 20 to said resistive and reactive circuits, each of 'said circuits being coupled to said tuned circuit and including provisions for connection individually to its respective resistive or reactive circuit, the coupling circuit for said resistive cir- 25 v cuit being coupled to said tuned circuit by two reactive couplings of opposite kind and also including therein two self-reactances of opposite kind. the coupling circuit for said reactive circuit being coupled to said tuned circuit by reactive coupling which includes one of the reactive cou- Dlings of said first named coupling circuit, the values of the reactive couplings and of the self-reactances of said first named coupling circuit being so proportioned relative to the im- 3 pedance .characteristic of said other coupling circuit that said resistive and reactive circuits produce substantially the same change in the resonant frequency of said tuned circuit when individually effectively connected to their respective coupling circuits, and that said firstnamed coupling circuit provides substantially. optimum coupling between said resistive circuit and said tuned circuit.

10. In combination, a tunable circuit adapted to be coupled alternatively to either of two circuits having respectively a mainly resistive and a mainly reactive impedance characteristic, and two coupling circuits corresponding, respectively, to said first-named circuits, each of said cir- 50 cuits being coupled to said tunable circuit and including provisions for connection to its respective first-named circuit, the impedance characteristics of said coupling circuits being so proportioned that the connection of either of said first-named circuits to its respective coupling circuit causes substantially the same effect on the resonant frequency of said tunable circuit for any adjustment of the resonant frequency of said to 11. In combination, two tunable circuits having coniointly actuated tuning elements, one of said .circuits being adaptedto be alternatively coupled to either of two circuits having respectively a mainly resistive and a mainly reactive c5 impedance characteristic, and two coupling circuits corresponding, respectively, to said secondnamed circuits, each of said coupling circuits being coupled to said one tunable circuit and including provisions for connection to its respective second-named circuit, the impedance characteristics of said coupling circuits being so proportioned that the connection of either secondnamed circuit to its respective coupling circuit causes such an effect on the resonant frequency of said resonant circuit, the values of capacitance f of said one tunable circuit as to maintain it substantially in a predetermined relation with the resonant frequency of the other of said tunable circuits for any adjustment of the resonant frequency thereof within its tuning range.

12. Incombination, a tunable circuit adapted to be coupled alternatively to eitherof two circuits having respectively a mainly resistive and a mainly reactive impedance characteristic, and two coupling circuits corresponding, respectively, to said first-named circuits, each of said circuits being coupled to said tunable circuit and including provisions for connection to its respective first-named circuit, the impedance characteristics of said coupling circuits being so proportioned that either, in connection with its respective firstnamed circuit, causes substantially the same ei feet on the resonant frequency of said tunable circuit and causes substantially optimum coupling of said resistive circuit to said tunable circuit when efiective, for any adjustment of the resonant frequency of said tunable circuit within the tuning range thereof.

13. In combination, a resonant circuit, including in series fixed inductance, fixed capacitance and variable capacitance, tunable over a wide range of frequency and adapted to be alternatively coupled to either a predetermined mainly resistive antenna or a predetermined mainly capacitive antenna; and two different fixed coupling circuits coupled to said resonant circuit and including provisions for connection respectively to said antennas, each coupling circuit including in series at least part of the reactance of said fixed capacitance, the coupling circuit for the resistive antenna including additionally in series individual fixed capacitance and individual fixed inductance inductively coupled to the fixed inductance and of self and mutual inductance in said coupling circuits being so proportioned that the resistive antenna coupling circuit has substantial capacitive reacta'uce at all frequencies in said range, and that the connection of either of said antennas to its respective coupling circuit causes substantially the same efiect on the resonant frequency oi said resonant circuit for any value of said variable capacitance is. In combination, a resonant circuit, including in series fixed inductance, :ilxed capacitance and variable capacitance, tunable over a wide range of frequency and adapted to be alternatively coupled to either a predetermined m m resistive antenna or a predeed mainly ca pacitive antenna; and two diflerent ed coupling circuits coupled to said resonant circuit and including provisions tor connection respectively to said antennas, each coupling circuit ineluding in series at least part of the reactance 5 of said fixed capmitance, the coupling circuit for the resistive antenna including additionally in series individual fixed capacitance and individual fixed inductance inductively coupled to the fixed inductance of said resonant circuit, the values of capacitance and of self and mutual inductance in said coupling circuits begso proportioned that the resistive antenna coupling circuit has substantial capacitive reactance at all frequencies in said range, that the connection of either or said antennas to its respective coupling circuit causes substantially the zal' e effect on the resonant frequency of said resonant circuit for any value of said variable capacitance, and that approximately optimum coupling is secured between said resistive tenna and said resonant circuit for any value oi said variable capacitance. 15. In a radio receiver having a plurality of tunable circuits withconjointly operated tuning elements, means for adapting saidrecelver for substantially optimum operation with either. a mainly capacitive antenna or a mainly resistive antenna without readjustment of the receiver, said means comprising two erent coupling circuits permanently coupled to the first tunable circuit of the receiver and adapted for connection respectively to said antennas, the coupling circuit for the capacitive antenna consisting of a capacitive reactance in common with said first tunable circuit, and the coupling circuit for the resistive antenna including at least a portion of said capacitive reactance and inclug also other reactances individual thereto including an inductive reactance inductively coupled to said first tunable circuit, the impedance characteristics of said resistive antenna coupling circuit being so proportioned that said resistive antenna is optimum coupled to said tunable circuit over the turnable range thereof, and that the coection of either antes to its restive i circuit. causes subs tially the same efiect on the resonant ire uency of said first circuit and on its relation to the rnant iueney of, the other or others oi circints, for a adiustment of the mar-rm. elt of d t 50 tlole circuit, 

